[Bug binutils/21266] New: Unstable qsort in bfd/elf64-ppc.c results in difference in ld's TLS opt 3 test on Windows

[pcarroll at codesourcery dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=21266

            Bug ID: 21266
           Summary: Unstable qsort in bfd/elf64-ppc.c results in
                    difference in ld's TLS opt 3 test on Windows
           Product: binutils
           Version: unspecified
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: pcarroll at codesourcery dot com
  Target Milestone: ---

The qsort() routine is noted to be unpredictable if 2 compared objects are
considered equal.  The 'compare_symbols' function in the bfd/elf64-ppc.c file
compares attributes of various symbols up to a point.  Where there can be a
problem is if there are 2 symbols with different names, but identical
attributes.  In this case, the current definition of 'compare_symbols' just
does a:
     return 0;
at the end of the function.  This, however, results in different behavior in
the TLS opt 3 testcase of the linker when the test suite is run on different
OSes.  A standard was created for that test case on Linux.  When this is run on
a Windows system, however, the test fails:

regexp_diff match failure
regexp "^00000000100000e8 <\.__tls_get_addr>:$"
line   "00000000100000e8 <.__tls_get_addr_opt>:"
regexp_diff match failure
regexp "^.*:    (4b ff ff ed|ed ff ff 4b)       bl      100000e8
<\.__tls_get_addr>$"
line   "    100000fc:   4b ff ff ed     bl      100000e8 <.__tls_get_addr_opt>"
regexp_diff match failure
regexp "^.*:    (4b ff ff e1|e1 ff ff 4b)       bl      100000e8
<\.__tls_get_addr>$"
line   "    10000108:   4b ff ff e1     bl      100000e8 <.__tls_get_addr_opt>"

To get predictable results between Linux and Windows, the last line of
'compare_symbols' should be changed to be:
     return strcmp(a->name,b->name);
With that change, if symbols have different attributes, then they continue to
be handled as before.
If, however, symbols are identical except for having different names (i.e., 2
symbols referring to the same location), then that will allow qsort() to
produce identical output for different OSes.

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